C. Durell 1 , S. Schiller 2 , D. Scharpf 1 , J. Holt 1 , B. Russell 1 Labsphere, Inc. 1 , Raytheon, Inc. 2 JACIE19 Workshop – Sept 24-26 Better Calibration | Better Data | Better Decisions On Demand Vicarious Calibration for Analysis Ready Data (ARD) – The FLARE Network
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On Demand Vicarious Calibration for Analysis Ready Data ... · IKONOS “Initial results for the vicarious calibration of Landsat 8 using the specular array radiometric calibration
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C. Durell1, S. Schiller2, D. Scharpf1, J. Holt1, B. Russell1
Labsphere, Inc.1, Raytheon, Inc.2
JACIE19 Workshop – Sept 24-26
Better Calibration | Better Data | Better Decisions
On Demand Vicarious Calibration for Analysis Ready Data (ARD) – The FLARE Network
Using too-small Lambertian target for DN• Sensor Calibration is Fundamental to the Future!• Bad or No Calibration = Data/Images are less valuable!
• Calibration is difficult & requires expert knowledge• Infrequent = low number of available sites• Uncertain = inconsistency of methods & within constellations• Expensive = national agencies & high cost assets needed
• Data Harmonization Hindered by Inconsistent Calibration• Sensor-to-sensor mismatch within a constellation• Space-to-airborne mismatch when harmonizing across platforms
• Shortcomings/Issues with Current Methods• Atmosphere is not constant & hard to measure in real time• Large area targets are often misused and don’t provide full calibration
results across all imaging platforms• No single method for airborne to space calibration convergence• Other types of sensor performance data are hard to get
• MTF/PSF difficult with normal terrestrial targets
Room for Improvement – Space and Airborne Image Quality
This document does not contain technology or technical data controlled under either the U.S. International Traffic in Arms Regulations or the U.S. Export Administration Regulations.
• The curvature of the spherical mirror scales down the brightness of the sun to an intensity that does not saturate the sensor focal plane.
“Initial results for the vicarious calibration of Landsat 8 using the specular array radiometric calibration (SPARC) method”, Schiller et al, SPIE 2016
• The Specular Array Calibration (SPARC) method allows any earth observing sensor to be calibrated to the solar spectral constant just like a solar radiometer.
• The mirror acts as a Field-of-View (FOV) aperture stop allowing the sun to be imaged directly as an absolute reference.
Watts/(m2 sr micron)/mirrorEo (λ) = Solar spectral constantR = Mirror radius of curvature (m)GSD = Line-of-site ground sample distance (m), cross-scan and along-scan
ρ (λ,θr) = Mirror specular reflectance at the reflectance angle θr
τ↓ (λ) = Sun to ground transmittance
τ↑ (λ) = Ground to sensor transmittance
“Initial results for the vicarious calibration of Landsat 8 using the specular array radiometric calibration (SPARC) method”, Schiller et al, SPIE 2016
)()(4)()()(),(),(
2
yGSDxGSDREL orrsensorat λλτλτθλρθλ ↑↓− =
Effective At-Sensor Radiance/Mirror (sensor and collection geometry specific)
Watts/( sr micron)/mirror
( ) ( ) )()(,),( 241 REI orTOAr λλτλτθλρθλ ↑↓=
TOA Intensity (Sensor Independent)
SPARC Radiative Transfer Equations Predicting At-sensor Intensity and Radiance
• The goal is to compare the vicarious SPARC predicted radiance to the sensor radiance reported in the Landsat 8 L1R calibrated imagery for individual targets
QuickbirdThe SPARC method has been applied to small footprint sensors demonstrating its capability to achieve <3% absolute uncertainty using an array of targets with different numbers of mirrors.
IKONOS
“Initial results for the vicarious calibration of Landsat 8 using the specular array radiometric calibration (SPARC) method”, Schiller et al, SPIE 2016
• Method has been demonstrated with IKONOS, Quickbird, Landsat and Sentinel
“Initial results for the vicarious calibration of Landsat 8 using the specular array radiometric calibration (SPARC) method”, Schiller et al, SPIE 2016
SPARC Calibration Panels:• Four 18” diameter mirrors on each
telescope mount (9 lbs each) • 10 m Radius of curvature mirrors• Clear Field-of-Regard (FOR) = 4.5o
• Deployed on a portable iOptron® iEQ45 ProTM alt-az telescope mount.
• Built-in 32-channel Global Positioning System (GPS).
• Payload mirror assembly on each mount is about 50 lbs
• Four deployable panels (each on separate mounts) are used to provide up to 3 calibration radiance levels in a single Landsat image collect.
Because SPARC targets are specular intensity sources and Landsat has a large GSD, the mirror radius of curvature is much larger than used with commercial sensors to produce the same effective radiance.
System level PSF shows negligible residuals when modeled as a Gaussian function.
“Initial results for the vicarious calibration of Landsat 8 using the specular array radiometric calibration (SPARC) method”, Schiller et al, SPIE 2016
Composite 2D PSF Profile Residuals show no outliers
Cross-scan and along-scan slices through the composite profile center
Sensor System Composite 2D PSF Profile For L8 Pan Band
• Calibration On-Demand – Look is scheduled, mirrors open and track• Precise instrumentation for Radiometric Ground-Truth (atmospheric correction)• Image data + FLARE ground truth data package = absolute radiometric calibration across all
sensor bands with GSD Specific system• Different bays can have different GSDs and independent tracking (serve multiple imagers)
Digital and Fully Automated
FLARE – Multiple “Bays” to Calibrate Multiple Imagers